1. Field of the Invention
The present invention relates to a bar code reader system for reading information from a micro-bar code which is reduced in size in comparison with known and currently available bar codes. More specifically, the invention relates to a bar code reader which can assure reading of information from the micro-bar code.
2. Description of the Related Art
As is well known, a bar code is designed to encode information, e.g. various characters, such as letters, figures, signs, by combination of a plurality of solid bars arranged in mutually parallel relationship to one another and blank intervals between the bars (which will be hereafter referred to as white bars). The following four types of bar codes are typically put into use.
(1) JAN (Japanese Article Number) Code
This coding system has been used for identification of consumer goods produced in Japan. The JAN coding system is compatible with UPC (Universal Product Code) used in the United States and EAN (European Article Number) used in Europe and Asia. In the JAN coding system, 13 digits of standard code and 8 digits of compressed code are available. The standard JAN code includes two digits of a country code, five digits of a product maker code, five digits of a product item code and one check digit. The compressed code has essentially the same code format to the standard code but has four digits of the product maker code and one digit of the, product item code. In the JAN coding system, only figures or numbers of 0.about.9 can be expressed by the combination of the solid bars and white bars. This coding system is convenient for a reading operation since it is not sensitive to scanning directions of a bar code reader.
(2) ITF (Interleaved Two of Five) Code
ITF coding system is a standard coding system adapted to physical distribution, which is established by adding a physical distribution identification code of 1 or 3 (including one leading digit which is normally 0) to the foregoing JAN code. Therefore, this ITF code may express only figures or numbers of 0.about.9. This coding system is successfully employed in the field of transportation. In addition, this coding system is employed as data for timed recording of a video tape recorder (VTR). The ITF coding system features high recording density and enables a stable information reading precision level even when the bar code is printed on a printing medium having a poor printing condition.
(3) CODE 39
In this coding system, one character is expressed by nine bars (four white bars between five solid bars). Among the nine bars, three bars, are thick solid or white bars having greater width. An asterisk (*) is employed as a start and stop code. This coding system makes it possible to express figures or numbers of 0.about.9, alphabetic letters of A.about.Z, various signs (e.g., +, -, blank space, /, $, %, .multidot.). This coding system has been employed as standard in industrial fields for factory automation. AIAG for U. S. automobile manufacturing and HIBC for U. S. hospitals and pharmaceutical industries are well known examples of this type of coding system.
(4) NW-7 (CODABAR)
In this coding system, one character is expressed by seven bars (three white bars between four solid bars). Among the seven bars, two or three bars are thicker bars. One of A, B, C and D is used as a start and stop code. This coding system is capable to express figures or numbers of 0.about.9 and various signs (e.g., +, -, blank space, /, $, %, .multidot.).
Bar code readers for reading information recorded on the bar codes, include CCD type bar code readers which read information employing charge-coupled devices (CCDs) and laser scanners which are adapted to scan the bar code ,with laser beams. For hand-held type bar code readers, the CCD type readers are frequently used due to reduction of size and weight and being less expensive.
Discussion will be given for one example of the conventional CCD type bar code reader with reference to FIGS. 10 to 12.
FIG. 10 shows the conventional bar code reader system 20 in operation. FIG. 11 is a diagrammatic illustration of an arrangement of components of an optical system employed in the conventional bar code reader of FIG. 10, as viewed from the front. FIG. 12 is a diagrammatic illustration of the optical system of FIG. 11 as viewed from the side. As can be seen from FIGS. 11 and 12, the bar code reader system comprises a CCD sensor 1, a focusing lens 2 and a pair of light emitting elements (which are aligned in the transverse direction relative to the plane of FIG. 12). The bar code reader 20 shown in FIG. 10 is designed to be gripped by a hand and to place the tip end onto a bar code 5a in an attitude perpendicular to a plane on which the bar code 5a is printed. By this, an image of the bar code 5a irradiated by the light beam from the light emitting elements is received by the CCD sensor 1 through the focusing lens 2 as reflected light. The image of the bar code 5a formed on the CCD sensor 1 is converted into electrical signals. Then the information contained in the bar code is decoded by a decoder (not shown).
The shown bar code reader 20 is particularly adapted to read information from a compressed size of bar code (hereafter referred to as "micro-bar code") which has a bar width of approximately 100 .mu.m of the thinnest solid bar, and the length of the bars is in a range of approximately 1.about.10 mm. In order to facilitate aligning of the beam axis 7 of the CCD sensor 1 in the bar code reader system 20 to the bar code 5a, a cut out 10 is formed at the tip end of the system 20.
However, when the micro-bar code is read by the bar code reader system 20 constructed as set forth above, the following problems are to be encountered. FIG. 13)a) is a diagrammatic illustration showing part of the bar code on an enlarged scale. Very high attention is paid to printing the bas codes. However, there are inherently caused defects in the solid bar, spots in the white bars and blurring or distortion of the solid, bars. When such defective bar code is scanned along three lines (1), (2) and (3) shown in FIG. 13(a) FIG 13(b)is timing chart showing the result of such scan through the lines (1), (2) and (3), in which an output signal becomes HIGH level when a solid bar is detected and LOW level when a white bar is detected. As is apparent from FIG. 13(b), the results are differentiated and contain a reading error .alpha. due to a defect of void V in the solid bar, the reading error .beta. due to blurring and a reading error .gamma. due to spot S in the white bar.
In addition, due to the presence of the cut out 10 at the tip end of the bar code reader system 20 in order to facilitate positioning thereof relative to the bar code 5a, external light may penetrate through the cut out 10 to cause variation of the intensity of the light received at the CCD sensor 1. Therefore, adjustment of the exposure period of the CCD sensor 1 is required. This extends the period required for decoding the information recorded on the bar code 5a and thus lowers efficiency the information reading operation.
Furthermore, it is possible for dust and dirt to penetrate through the cut out 10 to adhere to optical parts such as the light receiving surface of the CCD sensor 1 to make the information reading operation impossible.